chap 9 textbook notes

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Published on 20 Apr 2013
School
UTSG
Department
Psychology
Course
PSY280H1
CH9 PERCEIVING COLOR
Introduction to Color
Some functions of color vision
o Facilitate perceptual organization group elements, Gestalt
o Allow object discrimination, pick out objects in scenes
b/c enhances contrast of objects that’s similar in grayscale
o Evolutionary reason: color vision colored foods detection ability
suggested reason for color vision in monkey & humans
ex. picking berries easier w/ color vision
o Recognize & identify things easier
Ex. pink banana identification longer time than yellow banana
What colors do we perceive
o Can describe all perceivable colors w/ red, yellow, green, blue &
combinations of these 4 terms
Minimal amount of colors need to describe spectrum
Other colors (orange, violet, purple, brown) not needed
o EXTRASPECTRAL COLORS colors that do not appear in the spectrum
Ex. brown = mix of red & orange or yellow & black; purple = mix
of red & blue
o SATURATION access additional colors by adding/removing white,
i.e. changing the color’s saturation
Adding white = adding equal amounts to all wavelengths across
the spectrum, decrease saturation (DESATURATED)
o Change wavelength, intensity, saturation discriminable colors
Color and wavelength
o Perception of color associated w/ physical property of wavelength
Visible spectrum from short wavelength (400nm) to long
wavelength (700nm)
Wavelength bands w/i the range associated w/ diff colors
400 nm 450 nm = violet; 575 nm 590 nm = yellow
450 nm 490 nm = blue; 590 nm 620 nm = orange
500 nm 575 nm = green; 620 nm 700 nm = red
o Reflection and Transmission
COLORS OF LIGHT in spectrum related to their spectrum
Colors of object related to wavelengths of light reflected from
the objects into eyes
REFLECTANCE CURVES plots of percentage of light
reflected vs. wavelength
Note white & black paper reflect all wavelength equally
Note some objects reflect a dominate wavelength
CHROMATIC COLORS (HUES) some wavelengths of OPAQUE
OBJECTS are reflected more than others
ex. the hue (chromatic color) of tomato is red
SELECTIVE REFLECTION property of opaque objects that
reflect some wavelength more than others, characteristic
of chromatic colors
ACHROMATIC COLORS when reflection similar across
full spectrum (i.e. no hue) as w/ black, gray, white colors
SELECTIVE TRANSMISSION only some wavelength pass
through the TRANSPARENT OBJECTS or substances
Determines colors of transparent objects such as liquids,
plastic, glass ex. cranberry juice selectively transmit
long-wavelength light appears red
o ADDITIVE COLOR MIXTURE (mixing Light) when colored lights
superimposed, all the light that is reflect from the surface by each
light when alone is also reflected when the lights are superimposed
Summed together light contains all the wavelength from one
color combined with all the wavelength from the other color
o SUBTRACTIVE COLOR MIXTURE (mixing paint) when paints mixed,
both paints still absorb the same wavelength they absorbed when
alone, so the only wavelength reflect are those that are reflected by
both paints in common
Summed together paint absorbs all the wavelength from one
color and all the wavelength from the other color
Wavelength do not have color
o Colors are created by our perceptual system b/c we relate specific
colors to specific wavelengths
Connection btwn wavelength and the experience called “color”
is arbitrary
o Light rays are simply energy, nothing intrinsically “colored” about
wavelengths not physical property of an object Newton
Trichromatic theory of color vision
TRICHROMATIC THEORY OF COLOR VISION color vision depends on the
activity of three different receptor mechanisms
o Proposed by Thomas Young & Hermann von Helmholtz
Young (1802) proposed the theory based on findings that ppl w/
normal vision need at least 3 wavelengths to match any
wavelengths in “Test Field”
Later championed & refined by Helmholtz
Named YOUNG-HELMHOLTZ THEORY OF COLOR VISION
o based on results of psychophysical procedure (COLOR MATCHING)
o Central idea: color vision depends on three receptor mechanisms,
each w/ different spectral sensitivities
Light of particular wavelength stimulates 3 receptor
mechanisms in different degrees
Pattern of activity in 3 mechanisms result in perception of color
Each wavelength represented in nervous system by own pattern
of activity in the 3 receptor mechanisms
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Document Summary

Some functions of color vision: facilitate perceptual organization group elements, gestalt, allow object discrimination, pick out objects in scenes. B/c enhances contrast of objects that"s similar in grayscale. Selective transmission only some wavelength pass through the transparent objects or substances. Suggested reason for color vision in monkey & humans. Ex. picking berries easier w/ color vision: recognize & identify things easier. Ex. pink banana identification longer time than yellow banana superimposed, all the light that is reflect from the surface by each light when alone is also reflected when the lights are superimposed. Summed together light contains all the wavelength from one color combined with all the wavelength from the other color. What colors do we perceive: can describe all perceivable colors w/ red, yellow, green, blue & combinations of these 4 terms. Minimal amount of colors need to describe spectrum. Other colors (orange, violet, purple, brown) not needed: extraspectral colors colors that do not appear in the spectrum.

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